The present invention relates to a method of and apparatus for making stoppers of synthetic resin used for attaching price-labels and the like to wares or connecting a plurality of fibrous wares together.
Heretofore, the method of making stoppers for price-labels from synthetic resin, such as nylon, has been studied extensively. An original form of such stoppers was first introduced by the specification of U.S. Pat. No. 3,103,666 by Denisn Co., U.S.A., and thereafter various types of stoppers have been proposed. A stopper disclosed in the above U.S. Patent comprises a crossbar, a filament portion extending perpendicularly to said crossbar from its center and a head connected perpendicularly to said filament portion, to produce a deformed H-shape. A plurality of such stoppers are molded integrally in connected form. When said stoppers first developed each stopper was only molded integrally from sythetic resin. With such stopper it is necessary to make the filament portion as thin as possible so as not to damage cloth and other wares and also make them tough.
Because of the above requirements, the metal mold used for making stoppers is delicate, and burrs must be avoided in order to prevent damages of wares. One method of preventing production of burrs on a stopper is to increase the forming pressure of the metal mold; however since the metal mold has a fragile mold cavity, if the forming pressure is increased, the cavity portion of the mold will be deformed or in some cases the synthetic resin will leak through the contacting portions of the mold cavity thus resulting in the production of burrs.
These difficulties have thus caused serious problems in production of stoppers which have filament portions and which must not cause damage to wares.
For example, in the case where nylon is used, the material is melted at a temperature above the melting point thereof and then poured into the mold at a temperature below the melting point, the length of filament which can be satisfactorily molded is at most about 35 mm when the diameter of the filament portion is 1 mm. If this length is exceeded, burrs may be produced or the resin can not be readily poured into the metal mold. Also, the filament portion having a diameter of 1 mm tends to damage fibrous wares. Under such circumstances, if the diameter of the filament portion is about 0.6 mm, the length which is able to be molded is about 12.about.13 mm and in many stoppers the melted resin will not fill up to the head. The molded resin does not have molecular orientation, and therefore its strength is very low. Also it is brittle and in the filament form the resin is not suitable for use.
Accordingly, it has been proposed that the filament portion be subjected to stretching to make the diameter thereof thin thus increasing the strength.
As stretching methods for the filament portion of the stoppers, there are methods of stretching a molded blank of stoppers manually or automatically at room temperature or at a elevated temperature, and another method for using a metal mold and subjecting the molded blank to stretching immediately after the molding.
A method of stretching the filament portion of the stopper using a metal mold is known from, for example, Japanese Patent Application Publication No. 37,100/71. In this method, a split metal mold is used to mold and stretch the stopper blank, and has the advantage of avoiding the operation of removing the blank from the mold and feeding it to a stretching device.
The stretching of the filament portion produces the characteristic that the cross-sectional area thereof is reduced and the strength thereof increased greatly due to the molecular orientation, however there may be many cases wherein such features are a drawback. In other words, if the wares are attached with price-labels by means of stoppers, it is necessary to remove the label and stopper from the ware at the stage where the ware is purchased by a consumer. However, if the filament portion is substantially strengthened by stretching, it is difficult to remove the stopper from the wares and forcible removement will lead to damage of the wares.
Besides, these stretching methods have a substantial problem. In Japanese Patent Application Publication No. 37,100/71, as shown in FIGS. 6.about.8 of the Publication, the crossbar and head are seized by the abutting portions of the metal mold so as to effect stretching of the blank. Thus stretching tension must be applied to the whole length of the filament portion and if there is a relative weak portion in the filament portion, it may break off at that weak point.
Another problem in stretching by supporting both ends of the filament portion by the crossbar and head and applying tension to the portion, is that a larger stretching tension is necessary thus causing the stretching speed (moving speed of metal mold) to be increased too much. Further, if the timing of opening and closing of the metal mold is incorrect, the filament portion may be cut off and uneven stretching may occur.
In the manufacturing of synthetic fibres, the step of stretching fibres in the unstretched state is unavoidable. In this step it is important to make the diameter uniform and stretch at a high speed. Particularly, in the case of stretching fibres (bristles) of larger diameter, it is necessary to positively cause necking thereby making the stretched and unstretched portions distinct. Therefore attention has been directed on how to produce necking of desired shape at a desired position.
When comparing the stretching methods of synthetic fibres with that of Japanese Patent Application Publication No. 37,100/71, a substancial difference is recognized. Thus, in the Publication No. 37,100/71, the crossbar and head provided at both ends of the filament portion are caught by abutting portions of the metal mold and stretching is performed, so that there is no means of positively causing a stretching point, namely necking, resulting in easily producing uneven stretching. Particularly in the case where the filament portion is stretched with a part thereof being left in an unstretched state in order to adjust the length, the stretched part is not necessarily produced at a certain position, and the unstretched part may be produced, for example, at the center of the filament portion or near the crossbar.
The strength of the filament portion connected to the crossbar is very significant. Thus, if this portion is highly stretched, the strength will increase and the portion become thin. When it is guided through the needle of an attaching device, it can not be broken, and after the crossbar is passed through a ware, the filament portion is immediately extended and the crossbar returns to a position making a right angle to the filament portion.
The above problems can be summarized as follows:
(A) The filament portion of the stopper must be stretched at least at the portion near the crossbar.
(B) A plurality of filament portions of the stoppers must be stretched at the same time and uniformly.
(C) The filament portion of the stopper must have sufficient strength, but must have the property that it can be removed from wares easily.
(D) If an unstretched part is left in the filament portion of the stopper, it is desirably left as near the head as possible.
(E) In the stretching of the filament portion, it is necessary to make the stretching tension as low as possible so as not to cut the filament portion off or produce deformation of the crossbar.
Also the stretching method which can use a higher stretching speed must be used. It is also necessary to apply a stretching tension locally thereby reducing influence on the other part.